Converting an ATX 20/24PN P.S. to work with a Dell 8-Pin P.S. Motherboard.

[Dataman1]

Hi gang.. I have been idel forever - but I am back.
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I have a Dell Optiplex 9020 Motherboard that I am installing into a Full Tower Case.
The Dell Motherboard uses a Dell Proprietary 8-Pin (Mini-Fit Jr style connector).
The Dell Connector Pinout s as follows:
Pin 1 - +12VDC - White Wire
Pin 2 - +12VDC - White Wire
Pin 3 - COM/GND - Black Wire
Pin 4 - PS_ON -Green Wire
Pin 5 - +12 SB - - Purple Wire
Pin 6 - COM/GND - Black Wire
Pin 7 - COM/GND - Black Wire
Pin 8 - PWE_OK - Grey Wire.
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My problem is the Purple +5VSB (Pin 9 on ATX 20/24 Pin harness) wires on the ATX P.S. and the Purple +12 SB (pin 5) on the Dell 8-Pin Harness.
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I need the control the +12 SB Pin with the +5VSB Pin.
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So I found a simple Transistor 5V controlling 12 Volt Switch that was posted by BradtheRAD on this forum (but not discussing the Dell,Power Supply issue).
The Circuit is here:

https://obrazki.elektroda.pl/5651133400_1445836488_thumb.jpg

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My question is will this work to control the +12 SB using the ATX +5VSB? ?? Both signals do the same thing it is just that the ATX standard uses a +5V standarsd and Mchael Dell' people cose to use a +12V voltage reference. Little current is involved.

 

[FvM]

I fear you misunderstand ATX and Dell power supply operation. The controlling pin on ATX (and I guess also Dell) is PS_ON. 5V_SB is a permanent power supply.

 

[Dataman1]

FwM - thank you for your speedy reply...
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I am not misguided about the ATX Power Supply pins (the Dell 8-Pin is my only nemesis)
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The Power Supply is turned on by applying an active low (ground_ to PS_ON Pin 16 (this is a green wire).
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The PWR_OK Pin 8 ( Grey Wire) is simply an status signal that tells the Motherboard that the Power Supply is on and active and operating within parameters.
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+5VSB Pin 9 (Purple Wire) provides a 5VDC standby voltage to keeps certain circuits such as "Wake On LAN" or "Soft Power Start" to be active.
My issue is the +12 SB Pin 5 (purple Wire) of the Dell 8-Pin Power Supply Connector. If this is supplying +12V then a simple 5VDC to 12VDC converter will work.
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My problem is putting a 12V regulator in-line did not work. So it is not supplying 12VDC. So what is it looking for? If I use the circuit posted by BradtheRAD to run a 12Y pin from the +5VSB Pin should not the motherboard power up and stay powered up? Worst Case is that I can get +12V from one of the yellow wires - but is this what it really wants.
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My underlying problem is that Dell has Restricted their 7020 and 9020 Systems to a 290Watt Power Supply. My Tower will be running with a demand for a 520-Watt Power Supply (hence i want to use a 650-Watt or 850-Watt Power Supply.
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I do not want to Run two ATX Power Supplies (although the Full-Tower case I am using has an add-on option where Two Power Supplkies Mount (But I did not buy that option and it is a lot of sheet metal mods to make it Two power Supplies).
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Tried the 24-Pin to 8-Pin Converted - it worked, nut the system does not stay stable.
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I have Mini-Fit Jr connectors and Pins... I can simply Re-pin the ATX 20/24-Pin Connector the the Dell 8-Pin.
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My Problem is I cannot get Dell or anyone else to tell me what the +12 SB Pin 5 (Purple) wire signal is looking for .
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I think the ATX standard uses a +5V and Dell uses +12V. But my Dell P.S. is not putting out +12V or +5V on this pin. So ??????
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There has to be a resolution/solution I just have not found a good one.
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The ATX-20/24 Pin to 8-Pin solutions are not bullet proof and all of them have issues. I think it is the +12 SB Pin that is causing all the instabilities...
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I also find it hard that no one else on this Forum has come across this... Or they did and they simply went the Expensive Half-assed fix approach. But I want a fix. And I would like to keep all the available otions on the motherboard working. I hate half-assed work arounds (even though my approach may look like a half assed approach - My intention is to get to the core and come up with a Permanent Solution without spending $100s in do dads.

--- Updated Jan 28, 2025 ---

Still FvM - I appreciate your input...

 

[FvM]

I can't imagine how the Dell power supply should work without a standby supply. These points can be clarified by either analyzing a power supply schematic or a system in operation. I don't have Dell equipment, thus I can't.

 

[Dataman1]

Thanka FvM I email Michel Dell asking him to put me in contact with a Dell Technical/Engineer that can help me resolve my problems.
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Dell Tech Support is run by a bunch of Work At Home 20something age group... They know nothing about hardware - in fact durring the Optipley Motherboard scandal of last century I personally repaired 34,000 Optiplexes for Dell (they sent me pallets of Computers and I repaired them and sent 85% back - keeping the 15% to sell in our retail store).
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I also repaired 1400 Optiplexes for Honeywell in Phoenix, as well as 645 Optiplexes for Intell in Mesa, Arizona. I was literally swamped for two years and had to hire 28 Techs to help.
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This is a solveable problem - but I only have 9 Optiplex 9020s and three 7020s. All are in use in the office. I just ordered one on eBay - I plan to dissect this one.
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I am hoping Michel will provide me a realistically intelligent contact.
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I will ask him if Dell Uses the same IQ Test that the Federal Government seems to be using.
1st Question:
Write your name on a piece of paper- ten times.
(Note: For Credit for answering Question One you must get 3 out of ten Names Correct).
2nd Question:
Are you filling out this IQ test: Yes/Maybe/No
3rd Question: is someone else filling out this IQ Test for You: Yes/Maybe/No
4th Question:
Do you Know What an IQ Test is: Yes/Maybe/No
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Question one counts as 50% of test Score
Questions 2, 3 & 4 Count as 15% of test score each.
YOU MUST SCORE A MINIMAL OF 75% to GET THE JOB!

 

[Dataman1]

OK I have my answer.... Kind of....
The Pin 5 (+12 SB) with Purple Wire on the Dell mPS 8-Pin Plug is a 12VDC Standby Power Port. This supplies power for the WAKE ON LAN and Soft Start.
The PWR-OK (Pin 8) Grey wire on the Dell 8-Pin Power Plug is the same as the ATX 20/24-Pin Pin 8, Grey (also PWR_OK)
The PS-ON (Pin 4) Green Wire on the Dell PS Connector is the same as the ATX 20/24-Pin 16 (also green wire)
Pins 3, 6 and 7 on the Dell 8-Pin Power Plug are COM (Black) They can use Pin 7 (COM), Pin 16 (COM) and Pin 17 (BOM) all black leads.
Pins 1 and 2 (all white wires - but +12VDC) of the Dell 8-Pin Power Plug can taken from Pins 10 and 11 (=12V) Yellow Leads of the ATX 24-Pin Power Pl8g.
(Note I did not include the ATX 20-Pin because the Motherboard 20-Pin only has one +12V Pin)
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My problem is getting +12 SB (from Pin 5), a purple wire. But the ATX 20/24 Pin Power Plug uses a +5VSB instead of +12 SB. So the Dell Motherboard needs +12V for standby mode.... Funny thing is I am told this is about a 150mA to 250Ma average current draw with 500mSec peaks of 1-3 Amps... So it is postulated that the standard ATX +12V Yellow Leads used for a Hard Drive or Component Power can be used for this - But they would not supply +12V when powered down. )
This will require me to add a +5VSB Powered Adapter/P.S. that will use the +5VSB lead to turn a +12V DC Power Supply rated at say 1Amp (LM7812 comes to mind).
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The only issue is where to get +12 SB and controlling it with +5VSB... I am going to use a 15VAC 500mA Wall Wart to drive am LM7812 with an in-line transistor to turn it on/off) - When I get the Donor/Test PC I am going to verify if the +12 SB is active while the PC is on - if so I will simply wire in a +12VDC 500mA Wall wart and call it a day.
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For those out there wondering how I am going to get +3.3V and +5V to motherboard/CPU I do not have to... The motherboard supplies those (not the Power Supply). So I will simply open the Power Supply up and eliminate all the Orange 3.3V Leads by unsoldering them. (This will also make the P.S. Run Cooler - seriously have you ever looked into one of these? Its a rats nest of wires).
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Then I will simply power up my test PC and run it for a few weeks...

 

[FvM]

If +12SB is a standby power port, it's expected to provide permanent voltage like ATX +5VSB does. If it doesn't there's either a defect or an not yet understood prerequisite for using the Dell power supply.

Regarding PS_ON, I read in some sources that it's operation on Dell 8-pin connector would be inverted compared to ATX(+5V = on rather than 0V = on), but the info may be erroneous.

 

[Dataman1]

Thanks FvM....
My only problem is the +12SB... I need to provide 200mA to 650mA at 12VDC to this pin to keep the motherboard alive for Wake On Lan and Soft Start...
ATX Motherboards used +5VSB (+5Volts instead of the +12Volts that Dell Motherboards require).
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So I need to turn a +12V Regulator on and off using the +5V SB Pin.
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NOTE: Background########
1) I am going to use an ATX 850Watt Power Supply top power my Dell Optiplex 9020 Tower PC.
2) I have figured out that the Dell Motherboard does not get +3V for CPU Power From the Power Supply. It derives all the +3V and +5V voltages from the +12VDC Power provided by the Power Supply.
3) Actual CPU Power is provided by the 4-Pin Mini-Fit Jr Power Receptacle via the two +12VDC Power Pins.
4) the Dell motherboard is supplied +12VDC at 200-650mA to keep motherboard functions in stand by while the Motherboard is powered down. (The ATX Power Supplies provide +5V instead of +12V - so I need to turn a +12V power source on/off using +5V SB on the ATX Power Supply.
5) I can remove all the +3V Power leads from the ATX Power Supply - because they are not needed. To keep the Power Supply stable I will need to insert 1 ohm 3-Watt resistors across the +3V Rails to keep the P.S. Stable (as opposed to simply removing the +3V wires and leaving the rails open ( I am actually planning on using 1.2-Ohm 5-Watt resistors).
6) The Dell System only has an 8-Pin Mini-Fit Jr Power Receptacle and a 4-Pin Mini-Fit Jr Power Receptacle. The actual Dell Power Supply does not even have +5v&+12V Hard Drive/DVD Drive Power leads. (DVD and Hard Drive Power is taken off the motherboard). So the +5V and +12V Device Wiring can be sued for expansion (say DDS and HDD Power as well as Dual DVD/CD-RW Drives to be added. I can also add a SD card reader.. and most importantly power any added Power Hungry Video Drover card for my quad Displays.
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So there you have it - in a nut shell.
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But my problem is that Pesky +12 SB (to be controlled by the +5VSB pin.... on the ATX Power Supply).
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But I am confident that i will get it all to work.... (hopefully without frying my four spare Motherboards that I am using as Lab rats...)...

--- Updated Feb 6, 2025 ---

Final note: I absolutely hate just using a simple 24-Pin to 8-Pin adapter...
To me using the original ATX Power Supply wiring is just alot of +3V wires that are simply not needed..
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But then that's what happens when a 70+ Computer Geek that learned Computers on mainframes and built one of the first IMSAI 8088 Computers as well as one of the first Altair systems...
I speak UNIX, Lynx(by default), UniCode, Binary, Machine Language and Hexadecimal.
Not To mention HTML, SHTML, C-Code C+ and C++ as well as Java Script...
Robots does not need much more (but not that Pearl/ FORTRAN and PASCAL doesn't help - they just are not necessary to get Robotics systems up and running...
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So now I gave it all away - now everyone knows I am a cranky old-fart and legacy Geek...
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And Yes I FABRICATE/MAKE MY OWN PC BOARDS